G. L. Gaines, "On the History of Langmuir-Blodgett Films", First International Conference on Langmuir-Blodgett Films, Thin Solid Films, Vol. 99, pp. ix-xiii, 1983, provides a brief historical review of the early investigations of the monomolecular oriented films initially produced by the spreading of oils at a water-air interface and transferred to a support by dipping. Langmuir-Blodgett films (hereinafter also referred to as LB films) have been recently the subject of renewed investigations, since they offer an attractive approach for forming an assembly ranging from one to many superimposed layers, each layer being of monomolecular thickness and formed of molecules that are spatially aligned.
LB film assemblies are of particular interest in the fabrication of optical articles, including both those which have linear and nonlinear optical transmission properties. The preparation of an LB film assembly showing indications of nonlinear optical properties is reported by P. Stroeve, M. P. Sprinivasan, and B. G. Higgins, "Langmuir-Blodgett Multilayers of Polymer-Mercyanine-Dye Mixtures", Thin Solid Films, Vol. 146, pp. 209-220. LB films were formed of mixtures of merocyanine dyes and poly(methyl methacrylate).
Although LB films and film assemblies have drawn interest, there have remained some significant concerns. One of the concerns associated with LB film assemblies is the structural integrity and stability of the layers. Another concern relates to the areal definition of LB films. Since LB films are deposited by drawing a support through a liquid phase interface, initial deposition of the film often covers a greater area of the support than is wanted for a particular application. For example, in integrating an optical waveguide prepared as an LB film assembly with a semiconductor chip support containing an integrated circuit, it may be desirable to define precisely the areal interface of the semiconductor chip support and the waveguide.
Prior to the present invention attempts have been made to produce photopolymerized LB films. Garito U.S. Pat. No. 4,439,514 reports in Examples 24 and 25 the formation of LB films through the deposition of the diynes pentacosa-10,12-diynoic acid and N-d(+)(.alpha.-methylbenzyl)-10,12-pentacosadiynamide, respectively. While the UV and X-ray stimulated crosslinking of these monomers was reported to yield excellent pattern definition, radiation crosslinked diyne polymer films have suffered the disadvantage of physical imperfections (e.g., cracks and fissures). B. Tieke, G. Lieser and G. Wegner, "Polymerization of Diacetylenes in Multilayers", Journal of Polymer Science: Polymer Chemistry Edition, Vol. 17, pp. 1631-1644 (1979) is considered a cumulative teaching.
F. Nakanishi, S. Okada, and H. Nakanishi, "Photoreaction of Long-Chain Mono n-Alkyl Esters of p-Phenylenediacrylic Acid in Multilayer Films", Polymer Communications, Vol. 27, August 1986, pp. 238 and 239, reports the formation of LB films with mono alkyl esters of p-phenylenediacrylic acid followed by UV exposure. While some degree of insolubilization was reported by exposure, solubility of the exposed film, particularly in multilayer assemblies was reported. The formation of dimers, trimers, and possibly other oligomers as opposed to true crosslinked polymers is an explanation suggested for retained solubility.
H. Koch, A. Laschewsky, H. Ringsdorf, and K. Teng, "Photodimerization and Photopolymerization of Amphiphilic Cinnamic Acid Derivatives in Oriented Monolayers, Vesicles and Solution", Makromol. Chem., Vol. 187, pp. 1843-1853 (1986), reports investigations of UV exposure of amphiphiles containing a single cinnamic acid chain or two cinnamic acid chains linked through a head group. The single cinnamic acid chain monomers reacted intermolecularly to form dimers. The dual cinnamic acid chain compounds reacted intramolecularly without any significant change in molecular weight and to some extent intermolecularly to produce dimers, oligomers, and possibly some polymers.
E. Elbert, A. Laschewsky, and H. Ringsdorf, "Hydrophilic Spacer Groups in Polymerizable Lipids: Formation of Biomembrane Models from Bulk Polymerized Lipids", J. Am. Chem. Soc., Vol. 107, 1985, pp. 4134-4141, reports investigations of a variety of polymerizable lipids containing a poly(ethylene oxide) spacer group between a methacrylate reactive moiety and an amphiphilic structure consisting of two hydrophobic ligands joined through an amino nitrogen, a quaternized nitrogen, an ester, or a phosphate linking group. The formation of LB film assemblies is disclosed. UV exposure is reported to result in polymerization.